In power electronics, the trend is towards increasingly more powerful and increasingly fast turnoff components in order to be able to convert electrical powers with increasing efficiency, for example in converters or drives. Such components are, for example, the known GTOs, IGBTs or, alternatively, field-controlled thyristors (FCThs) or static induction thyristors (SIThs).
In this connection, particular difficulties are also presented by the drive of GTOs in particular, because in these components, critical states which usually have to be avoided in the prior art by a complex external protective circuit, the so-called "snubbers", may be assumed as a result of inhomogeneous turn-on and turn-off. However, such "snubbers" not only make the circuit more expensive, but also require appreciable space and cause an additional power loss.
Very recently it has therefore been proposed (EP-A1-0 489 945) to reduce the protective-circuit complexity in GTOs by driving the specified components by a specially designed gate unit in a "hard" mode, ie. with very steep and high gate pulses for the turn-on and turn-off. The object of these proposals was to manage, if possible, without modifying the GTO itself and its housing so that the existing, commercially available components, such as are described in the publication mentioned at the outset, can also continue to be used.
Although it has already been possible to achieve appreciable improvements in the use of GTOs in this manner, further advantages can be achieved, in particular, if measures are also permitted in the internal structure of the components themselves. Of importance in this connection is, in particular, the mutual inductance between the GTO and its gate unit, which mutual inductance decisively impedes the "hard" drive and makes complex gate units necessary in the case of unduly high values, such as are caused by conventionally bringing out the gate lead through the insulating housing. To simplify the gate unit and also to reduce its volume and current consumption, a drastic reduction in the mutual inductance between GTO and gate unit from the existing value of about 30 nH to values of .ltoreq.2 nH is therefore desirable.
For FCThs, in particular, but also for GTOs, solutions in which the incorporation of the most important components of the gate unit directly in the component housing is envisaged (in this connection see: EP-A1-0 328 778 or EP-A1-0 381 849) have already been proposed for reducing the mutual inductance. Although such an incorporation results in very low connection inductances, it entails not only high development and manufacturing costs but also a number of impediments, such as:
the lack of availability of suitable pulse capacitors which provide the necessary capacitance values and the required reliability even at the high temperatures; PA1 the lack of reliability of the internal contact in the component; PA1 the need to screen the drive circuit as protection against coupling-in from the main circuit; and PA1 the need to have to connect, furthermore, a turn-on circuit (possibly in the housing) and a holding circuit for generating a continuous gate current in the ON state in addition to the turn-off circuit if GTOs are used, in which connection there would still hardly be room in the housing for the holding circuit because of the necessary currents. PA1 (a) the gate lead is of rotationally symmetrical design and is disposed concentrically with respect to the cathode contact; and PA1 (b) the gate lead is electrically isolated from the cathode contact by a single insulator.
For the reasons mentioned, a part of the gate unit would still have to be disposed outside the GTO housing in the known solution.